The declining costs of single-board computers has made serious computing power available for even the most trivial of tasks. It’s easy enough to slap a Raspberry Pi onto almost anything for nearly the same cost as a powerful 32-bit microcontroller platform, but this takes some of the fun out of projects for a few of us. Looking to get into the weeds can be a challenge as well, as [Michal Zalewski] demonstrates in this audio playback device he built from a simple 8-bit microcontroller.
The small toy takes audio input from a microphone through an op-amp and feeds this signal to an ADC within the AVR128DA28 microcontroller. The data is then stored on a separate memory chip ready to be played back through another op-amp paired with a speaker. This is where being familiar with the inner workings of the microcontroller comes in handy. By manipulating the interrupt routines in specific ways, the audio stored in memory can be played back at various speeds.
[Michal] intended this build to be a toy for one of his younger relatives, and for the price of a few ICs and buttons it does a pretty good job of turning a regular voice into a chipmunk voice like some commercial children’s toys some of us might remember. If the design aesthetics of this gadget look familiar, you may be thinking of his minimalist gaming device which we recently featured.
If you’ve ever seen those gadgets with the “breathing light” LEDs on them and wondered how to do it, then [DIY GUY Chris] can show you how to design your own surface-mount version, using only analogue electronics.
The circuit itself is built around a slow triangular-wave oscillator, that ramps the current up and down in the LEDs to make it look as if the lights are breathing in and out. The overall effect is rather pleasing, and the oscillation speed can be adjusted using the on-board potentiometer.
This project is actually an update to a previous version that used through-hole components (also shown in the video below), and goes to show that revisiting completed projects can give them a new lease of life. It also shows how easy it has become to design and order custom circuit boards these days. It’s not so long ago that a project like this would have been either made on stripboard or etched from copper-plated FR4 in a bubbling tank of acid!
If you have revisited an old project that you’re proud of and would like to show others, why not drop us a message on our tips line?
“Don’t worry, that’ll buff right out.” Alarming news this week as the James Webb Space Telescope team announced that a meteoroid had hit the space observatory’s massive primary mirror. While far from unexpected, the strike on mirror segment C3 (the sixth mirror from the top going clockwise, roughly in the “south southeast” position) that occurred back in late May was larger than any of the simulations or test strikes performed on Earth prior to launch. It was also not part of any known meteoroid storm in the telescope’s orbit; if it had been, controllers would have been able to maneuver the spacecraft to protect the gold-plated beryllium segments. The rogue space rock apparently did enough damage to be noticeable in the data coming back from the telescope and to require adjustment to the position of the mirror segment. While it certainly won’t be the last time this happens, it would have been nice to see one picture from Webb before it started accumulating hits.
[Robo] over at Tiny Transistor Labs has a fascinating look at what’s inside these modern, ultra low-power devices that consume absolutely minuscule amounts of current. Crank up the magnification, and go take a look at the dies on these two similar (but internally very different) devices.
The first unit is the Texas Instruments LPV801, a single-channel op-amp that might not be very fast, but makes up for it by consuming only a few hundred nanoamps. Inside, [Robo] points out all the elements of the design, explaining how a part like this would be laser-trimmed to ensure it performs within specifications.
The second part is the Texas Instruments LPV821 which uses a wee bit more power, but makes up for it with a few extra features like zero-drift and EMI hardening. Peeking inside this device reveals the different manufacturing process this part used, and [Robo] points out things like the apparent lack of fuses for precise trimming of the part during the manufacturing process.
Seeing these structures up close isn’t an everyday thing for most of us, so take the opportunity to check out [Robo]’s photos. Tiny Transistor Labs definitely takes the “tiny” part of their name seriously, as we’ve seen with their 555 timer, recreated with discrete transistors, all crammed into a package that’s even the same basic size as the original.
Hurricane season is rapidly approaching those of us who live in the northern hemisphere. While that does come with a good deal of stress for any homeowners who live in the potential paths of storms it also comes with some opportunities for treasure hunting. Storms tend to wash up all kinds of things from the sea, and if you are equipped with this DIY metal detector you could be unearthing all kinds of interesting tchotchkes from the depths this year.
The metal detector comes to us from [mircemk] who is known for building simple yet effective metal detectors. Unlike his previous builds, this one uses only a single integrated circuit, the TL804 operational amplifier. It also works on the principle of beat-balance which is an amalgamation of two unique methods of detecting metal. When the wire coils detect a piece of metal in the ground, the information is fed to an earpiece through an audio jack which rounds out this straightforward build.
[mircemk] reports that this metal detector can detect small objects like coins up to 15 cm deep, and larger metal objects up to 50 cm. Of course, to build this you will also need the support components, wire, and time to tune the circuit. All things considered, though it’s a great entryway into the hobby.
We’re all aware that there are plenty of fake components to be found if you’re prepared to look in the right places, and that perhaps too-good-to-be-true chip offers on auction sites might turn out to have markings which rub off to reveal something completely different underneath. [IMSAI Guy] saw a batch of OP-07 laser-trimmed op-amps at a bargain price, so picked them up for an investigation. You can take a look at the video below the break.
A perfect op-amp has a zero volt output when both of its inputs are at the same voltage, but in practice no real device approaches this level of perfection. It’s referred to as the offset voltage, and for instrumentation work where a low offset voltage is important there are parts such as the OP-07 which have each been adjusted using a laser to trim their components for the lowest offset. This process is expensive, so naturally so are genuine OP-07s.
Identifying real versus fake op-amps in this case is as simple as hooking the chip up as a unity gain non-inverting amplifier and measuring the voltage on the output (we can’t help a tinge of envy at that Keithley 2015 THD multimeter!), from which measurement the fakes should be clearly visible. First up are some 741s with their > 1 mV offsets (though an outlier 741 had a 40μV offset) to show what a cheap op-amp could be expected to do, then we see the OP-07s. Immediately with an offset of > 1.2 mV we can tell that they’re fake, which as he admits for the price is hardly a surprise. Meanwhile we’ll keep an eye out for Korean-made 741s like the outlier low-offset device.
We don’t see many EMG (electromyography) projects, despite how cool the applications can be. This may be because of technical difficulties with seeing the tiny muscular electrical signals amongst the noise, it could be the difficulty of interpreting any signal you do find. Regardless, [hut] has been striving forwards with a stream of prototypes, culminating in the aptly named ‘Prototype 8’
The current prototype uses a main power board hosting an Arduino Nano 33 BLE Sense, as well as a boost converter to pump up the AAA battery to provide 5 volts for the Arduino and a selection of connected EMG amplifier units. The EMG sensor is based around the INA128 instrumentation amplifier, in a pretty straightforward configuration. The EMG samples along with data from the IMU on the Nano 33 BLE Sense, are passed along to a connected PC via Bluetooth, running the PsyLink software stack. This is based on Python, using the BLE-GATT library for BT comms, PynPut handing the PC input devices (to emit keyboard and mouse events) and tensorflow for the machine learning side of things. The idea is to use machine learning from the EMG data to associate with a specific user interface event (such as a keypress) and with a little training, be able to play games on the PC with just hand/arm gestures. IMU data are used to augment this, but in this demo, that’s not totally clear.
All hardware and software can be found on the project codeberg page, which did make us double-take as to why GnuRadio was being used, but thinking about it, it’s really good for signal processing and visualization. What a good idea!
Obviously there are many other use cases for such a EMG controlled input device, but who doesn’t want to play Mario Kart, you know, for science?